1. Field of the Invention
The present invention relates generally to medical diagnostic methods and apparatus and, more particularly, to methods and apparatus for the non-invasive sensing of blood glucose levels.
2. Description of the Prior Art
In the treatment of diabetes, it is oftentimes necessary for the afflicted patient to periodically monitor his or her blood glucose level and then administer appropriate amounts of insulin in response to the glucose level so determined. Heretofore, it has been common to employ a pin prick to the finger in order to draw a blood specimen to determine the glucose level. More recently, non-invasive tests have been developed for this purpose.
It is generally known in the art that radiation, particularly near-infrared radiation over a range of wavelengths, can be projected in a non-invasive manner on a portion of the body of a patient. The resulting radiation emitted from that portion of the body, either scattered or transmitted after absorption and scattering, can be detected and processed to derive an expression of the detected radiation as a function of wavelength and, therefrom, the concentration of blood glucose. Since the detected radiation is a continuous signal covering all of the wavelengths in the range of interest, it is necessary for further analysis to separate the intensities of radiation at the various individual wavelengths, or smaller bands of wavelengths, to extract the desired blood glucose level information.
U.S. Pat. Nos. 5,070,874 and 5,460,177 describe methods for the non-invasive measurement of blood glucose levels. In general, these methods use a spectrophotometer to measure the absorbency of the near-infrared radiation at different wavelengths across the range of interest. The absorbency plotted against the wavelengths constitutes a spectrum. By analyzing the spectrum, the blood glucose levels, or changes thereto, can be determined. As the blood glucose levels vary, the detected spectrum changes slightly.
In order to make the measurements discussed above, the radiation must be transmitted from a radiation source via a sensor head to the skin of a patient and the detected radiation received back from the skin must be collected at the sensor head and carried to a spectrophotometer for further analysis. When making such fine spectral skin measurements, the sensor system measures only a small area of skin which is in intimate contact with the sensor head. Human skin consists of biological components that may be different from point to point over a given area. There may be, for example, certain types of skin cells or hair follicles that vary in composition over a given area of skin. Accordingly, a single, non-invasive measurement of blood glucose level within a given area will vary as greatly as the skin composition itself.
It is an object of the present invention to account for the naturally occurring biological skin variations of a patient so as to permit non-invasive glucose measurement of greatly enhanced reliability and accuracy. It is a further object to provide an apparatus and method which permits self testing by the diabetes patient without the need for specialized clinical assistance.